The present invention relates to devices and methods for removing a sample of tissue from a human or animal. In particular, the present invention pertains to devices and methods for conducting a biopsy to remove a sample or specimen of a tumor or lesion for examination and analysis.
In diagnosing and treating certain medical conditions, such as potentially cancerous tumors, it may be desirable to extract from a portion of suspicious tissue, such as a tumor, a specimen of the suspicious tissue for detailed examination and analysis. The process of removing such a specimen of tissue is referred to as a biopsy.
In many instances, the suspicious tissue to be examined is inside the patient's body. For example, the suspicious tissue may be a tumor inside a human breast. To minimize surgical intrusion into the body, it is desirable to be able to insert a small instrument into the body for extracting a portion of the suspicious tissue.
Different types of instruments and procedures have been developed for conducting biopsies to extract a tissue specimen for analysis. One device that has been developed is the fine needle aspirator. This device comprises a hollow needle, the end of which is sharpened. The needle is inserted into the suspicious tissue so that individual cells or clusters of cells of the tissue lodge inside the hollow core of the needle. The needle is then extracted from the patient, and the cells and fluid removed from the needle for a cytological examination. In certain circumstances, however, it may be desirable to extract portions of tissue for a histological examination, a procedure that is not typically feasible using a fine needle aspirator.
Another type of tissue-sampling device for biopsies is exemplified by the device described in U.S. Pat. No. Re.34,056—Lindgren et al. This type of device includes a forward stylet, which includes at its distal end a sharpened cutting surface. The stylet may be, for example, a needle sized between 12 and 20 gauge. Behind the sharpened cutting end of the stylet, along the shaft thereof, is a groove. A hollow cannula surrounds the stylet, and has its distal end sharpened to form a fine cutting edge. A mechanism is provided to move the stylet and the cannula forward separately. For example, springs may be used for this purpose. Preferably, the stylet and the cannula are moved forward rapidly so that the sharpened ends thereof may efficiently cut the tissue. In operation, the operator of this type of device first causes the stylet to be pushed forward through the tumor or suspect tissue. After the distal end of the stylet has passed through the suspect tissue, a portion of the tissue surrounding the stylet partially fills the groove on the shaft of the stylet. The cannula is then pushed forward so that the sharpened distal end of the cannula cuts off the portion of the tissue that has filled the groove on the shaft of the stylet, and encloses that tissue. The entire device may then be removed from the patient's body, and the tissue trapped in the cannula removed for examination and analysis.
U.S. Pat. No. 5,526,822—Burbank et al. discloses another type of biopsy device that includes the ability to apply a vacuum to the groove in the stylet. This vacuum assists in drawing tissue into the groove, ensuring that a more substantial portion of tissue is severed by the cutting cannula. Using such a system, it is in some cases possible to use a relatively large stylet (e.g., a 7 to 14 gauge needle) to obtain a relatively large tissue sample.
All of the above-described systems use knife edges to a cut the tissue. The cutting edge must remain extremely sharp, so that it cuts the tissue cleanly. Moreover, the stylet and the cannula cutter must be propelled forward rapidly to provide a clean cut through the tissue. Elaborate mechanisms are typically employed to provide the rapid forward movement. Because the knife edges move rapidly, however, there is limited time for tissue to fill the groove on the stylet. Therefore, the system sometimes obtains a smaller sample than would be ideal. In addition, variations in tissue density and anatomy may cause the stylet to deflect from its ideal position in relation to the tissue to be penetrated.
Electrosurgical techniques have been used in a variety of circumstances, including certain types of biopsies. In electrosurgery, high frequency electrical energy is applied through a primary electrode to tissue. The electrical energy flows through the tissue to a return electrode. The tissue adjacent to the primary electrode is ablated, to form an opening in the tissue. The return electrode in monopolar electrosurgery may be a large electrode placed on the exterior of the patient's body at a point remote from the primary electrode. In bipolar electrosurgery, the return electrode may be a smaller electrode positioned somewhat near the primary electrode. An exemplary biopsy instrument using electrosurgical techniques is described in International Publication No. WO 98/08441.